The Feedback Amplifier is amplifier, which use Feedback network, generally for improving performance (gain stability, linearity, frequency responce etc). Feedback can be negative or positive. Negative feedback (NFB), firstly invented by H. S. Black (pat. 2,102,671), as a rule, much more useful. Main (and great) idea of this invention is simple: if NFB depth are big, overall responce of whole system can be very close to inverted feedback network response. As feedback network can be simple an passive, high degree of its stability and linearity can be obtained. Most widely known realisation of this principle in electronics are circuits, based on Operational Amplifiers (Op-Amps), such as old uA741 or LF411. This (and many other) operational amplifiers designed such way, what overall characteristics defined mainly by feedback hetwork.
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